From bf4588d0c394f60786161c36506f799e7007b077 Mon Sep 17 00:00:00 2001
From: Zefram <zefram@fysh.org>
Date: Thu, 22 Aug 2013 22:57:01 +0100
Subject: [PATCH] detect Carp/Carp::Heavy version mismatch

[rt.cpan.org #79649]  If an old Carp, requiring old-style Carp::Heavy
that provides subroutines, gets a newer stub-style Carp::Heavy, due to
@INC having changed, the resulting error messages were not awesome.
---
 MANIFEST                     | 1 +
 dist/Carp/lib/Carp/Heavy.pm  | 5 +++++
 dist/Carp/t/heavy_mismatch.t | 8 ++++++++
 pod/perldelta.pod            | 5 ++++-
 4 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 dist/Carp/t/heavy_mismatch.t

diff --git a/MANIFEST b/MANIFEST
index cad6c18..b11bee4 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -2986,6 +2986,7 @@ dist/Carp/t/baduni.t		See if Carp handles non-char Unicode
 dist/Carp/t/baduni_warnings.t		See if Carp handles non-char Unicode when loaded via warnings.pm
 dist/Carp/t/Carp_overload.t		See if Carp handles overloads
 dist/Carp/t/Carp.t		See if Carp works
+dist/Carp/t/heavy_mismatch.t		See if Carp::Heavy catches version mismatch
 dist/Carp/t/heavy.t		See if Carp::Heavy works
 dist/Carp/t/stash_deletion.t		See if Carp handles stash deletion
 dist/Carp/t/swash.t		See if Carp avoids breaking swash loading
diff --git a/dist/Carp/lib/Carp/Heavy.pm b/dist/Carp/lib/Carp/Heavy.pm
index f0de263..f8c409e 100644
--- a/dist/Carp/lib/Carp/Heavy.pm
+++ b/dist/Carp/lib/Carp/Heavy.pm
@@ -4,6 +4,11 @@ use Carp ();
 
 our $VERSION = '1.32';
 
+my $cv = defined($Carp::VERSION) ? $Carp::VERSION : "undef";
+if($cv ne $VERSION) {
+	die "Version mismatch between Carp $cv ($INC{q(Carp.pm)}) and Carp::Heavy $VERSION ($INC{q(Carp/Heavy.pm)}).  Did you alter \@INC after Carp was loaded?\n";
+}
+
 1;
 
 # Most of the machinery of Carp used to be here.
diff --git a/dist/Carp/t/heavy_mismatch.t b/dist/Carp/t/heavy_mismatch.t
new file mode 100644
index 0000000..233bc5a
--- /dev/null
+++ b/dist/Carp/t/heavy_mismatch.t
@@ -0,0 +1,8 @@
+print "1..1\n";
+
+$INC{"Carp.pm"} = "<faked>";
+$Carp::VERSION = "0.90";
+eval { require Carp::Heavy; };
+print $@ =~ /\AVersion mismatch between Carp 0\.90 \(<faked>\) and Carp::Heavy [0-9._]+ \(.+\)\.  Did you alter \@INC after Carp was loaded\?\n/ ? "" : "not ", "ok 1\n";
+
+1;
diff --git a/pod/perldelta.pod b/pod/perldelta.pod
index cc9ba6d..2a5fd5f 100644
--- a/pod/perldelta.pod
+++ b/pod/perldelta.pod
@@ -121,10 +121,13 @@ XXX
 
 L<Carp> has been upgraded from version 1.31 to 1.32.
 
-Carp now won't vivify the C<overload::StrVal> glob or subroutine or the
+C<Carp> now won't vivify the C<overload::StrVal> glob or subroutine or the
 C<overload> stash.
 It also avoids some unwanted Unicode warnings on older Perls (which
 doesn't affect behaviour with current Perl).
+C<Carp::Heavy> detects version mismatch with C<Carp>, to give a good
+error message if a current (stub) C<Carp::Heavy> gets loaded by an old
+C<Carp> that expects C<Carp::Heavy> to provide subroutines.
 
 =item *
 
-- 
2.7.4